From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 84D76C7618F for ; Tue, 16 Jul 2019 17:19:07 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 573942173C for ; Tue, 16 Jul 2019 17:19:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 573942173C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:51394 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnR6Y-0006qg-6f for qemu-devel@archiver.kernel.org; Tue, 16 Jul 2019 13:19:06 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38900) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnR6O-0006O6-Tv for qemu-devel@nongnu.org; Tue, 16 Jul 2019 13:18:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hnR6N-0005FR-Sc for qemu-devel@nongnu.org; Tue, 16 Jul 2019 13:18:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55974) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hnR6L-0005Cx-Ne; Tue, 16 Jul 2019 13:18:53 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4BC8C302246A; Tue, 16 Jul 2019 17:18:52 +0000 (UTC) Received: from linux.fritz.box (ovpn-117-24.ams2.redhat.com [10.36.117.24]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 391885E7A5; Tue, 16 Jul 2019 17:18:51 +0000 (UTC) Date: Tue, 16 Jul 2019 19:18:49 +0200 From: Kevin Wolf To: Max Reitz Message-ID: <20190716171849.GL7297@linux.fritz.box> References: <20190703172813.6868-1-mreitz@redhat.com> <20190703172813.6868-6-mreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190703172813.6868-6-mreitz@redhat.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Tue, 16 Jul 2019 17:18:52 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 05/12] block: Reduce (un)drains when replacing a child X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 03.07.2019 um 19:28 hat Max Reitz geschrieben: > Currently, bdrv_replace_child_noperm() undrains the parent until it is > completely undrained, then re-drains it after attaching the new child > node. > > This is a problem with bdrv_drop_intermediate(): We want to keep the > whole subtree drained, including parents, while the operation is > under way. bdrv_replace_child_noperm() breaks this by allowing every > parent to become unquiesced briefly, and then redraining it. > > In fact, there is no reason why the parent should become unquiesced and > be allowed to submit requests to the new child node if that new node is > supposed to be kept drained. So if anything, we have to drain the > parent before detaching the old child node. Conversely, we have to > undrain it only after attaching the new child node. > > Thus, change the whole drain algorithm here: Calculate the number of > times we have to drain/undrain the parent before replacing the child > node then drain it (if necessary), replace the child node, and then > undrain it. > > Signed-off-by: Max Reitz I think this looks good (and fixes a bug that Denis Plotnikov reported before while trying to fix IDE submitting requests in a drained section), but I would be even more confident if we could add tests for the various cases to tests/test-bdrv-drain.c. Kevin